Anaerobic co-digestion of Unavoidable and Avoidable Food-Waste with addition of eggshells and applied kinetic studies

Abstract

Food waste is a growing concern due to its contribution to harmful greenhouse gas (GHG) emissions. To address this issue, anaerobic digestion (AD) has been identified as an effective and sustainable method to treat organic waste. This study aimed to investigate the anaerobic co-digestion of avoidable and unavoidable food waste, along with calcined and uncalcined eggshells, using fresh cow dung as an inoculum in a 1:1 ratio. The use of eggshells in this study was based on their ability to preserve carbohydrates due to the presence of Ca(OH)2, an alkaline additive. The study was carried out in a batch process (1 L) at a mesophilic temperature range of 35 ± 2 °C, and kinetic parameters during biogas production were predicted by the first-order and modified Gompertz model. The results showed that the volatile solids % of food waste was reduced, indicating gas production during the process. However, the gas composition showed a negligible amount of methane production, likely due to the rise in pH caused by the addition of calcined eggshells, which inhibited the completion of the methanogenesis process. The decrease in the Volatile solids content was attributed to the addition of uncalcined eggshells, which requires a higher temperature (1000 °C) to calcine completely. The maximum biogas yields, predicted by the first order and the modified Gompertz model, are 1235 mL/gVS (experimental 1195 mL/gVS) and 1185 mL/gVS, respectively. However, the addition of eggshells to the co-digestion process must be carefully monitored to maintain the pH balance. Overall, this study suggests that the co-digestion of food waste and adding eggshells can be a viable and promising solution to food waste management to recover energy from it.